Small Craft Advisory 857, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
200 PM ADT TUE SEP 19 2006

.DISCUSSION...
MODELS HAVE MADE A MAJOR SHIFT FROM YESTERDAY. 12Z RUNS HAVE FULLY
MERGED TO THE OVERNIGHT 00Z SOLUTIONS. ENSEMBLE MEANS FROM THE 00Z
GFS AND CANADIAN IN ADDITION TO THE ECMWF ALSO AGREE WITH THIS
SOLUTION. IN FACT THE UKMET AND 12Z ENSEMBLE MEAN HAVE SIMILAR PATHS
A BIT FARTHER WEST THAN THE OPERATIONAL GFS AND SIGNIFICANTLY FARTHER
WEST THAN THE NAM. BELIEVING THE CURVATURE...WE HAVE LEANED HEAVILY
TO THE NEW UKMET WHICH IS A BIT FARTHER WEST IN ITS TRACK. THE
DIFFERENCE IS THAT THE GFS LOW IS EAST OF THE ALEUTIAN RANGE TO
DENALI WHEREAS THE OTHERS ARE HEADING TO THE LOWER KUSKOKWIM VALLEY.
THE SHIFT IN MODEL SOLUTIONS IS DUE TO THE AMPLIFICATION OF THE
TROUGH IN THE BERING SEA AS OPPOSED TO YESTERDAYS SOLUTIONS. THIS WAS
CAUSED BY THE SHORT WAVE TROUGH OVER THE BERING SEA BEING STRONGER
THAN ANTICIPATED. THEREFORE THE TROUGH IS DUG OUT DEEPER IN THE
BERING MAKING A LARGER AMPLITUDE RIDGE IN THE GULF THUS PULLING THE
NEXT DEVELOPING LOW MUCH FARTHER WEST. THIS STRONG UPPER LOW OVER THE
ALASKA PENINSULA THURSDAY WILL PUSH NORTHEAST AND KNOCK DOWN THE
RIDGE OVER THE GULF FRIDAY AND PUSH IT TO THE SOUTHERN PANHANDLE. A
SERIES OF SHORT WAVE TROUGHS BEHIND IT WILL KEEP THE RIDGE AT BAY. IN
THE MEANTIME...A BROAD TROUGH WILL DEVELOP OVER THE ENTIRE AREA
FRIDAY WHICH WILL REMAIN INTO SUNDAY. THIS IS CARVED OUT BY A LOW
MOVING OUT OF THE ARCTIC OCEAN AND KAMCHATKA PENINSULA MOVING INTO
THE BERING SEA BEHIND THIS WEAKENING LOW OVER THE INTERIOR. THESE
FEATURES ACT TO LIFT THE INTERIOR LOW TO THE YUKON AND ALLOW THE
RIDGE TO BUILD BACK A BIT IN THE PANHANDLE.

SURFACE EAST OF THE ALASKA RANGE...CURRENT LOW OVER KODIAK TO WEAKEN
AND MOVE TO THE EASTERN NORTHERN GULF COAST TONIGHT AND INLAND
TOMORROW. SOME STRONG WINDS ALONG THE NORTHERN GULF COAST WITH THE
ASSOCIATED FRONT. WINDS WILL DIMINISH THIS EVENING AS THE LOW MOVES
INLAND. HOWEVER...AS THE LOW CENTER MOVES TO THE EASTERN
GULF...EXPECT WINDS TO SWITCH TO THE WEST AND REMAIN MODERATE TO THE
LOW MOVES INLAND TOMORROW AFTERNOON/EVENING. PRECIPITATION WILL
SPREAD FROM THE COAST INLAND TONIGHT WITH DOWNSLOPE WIND EFFECT
LESSENING. SHOWERS WILL REMAIN INTO WEDNESDAY AS ENOUGH MOISTURE AND
INSTABILITY REMAIN. HIGH PRESSURE MOVES OVER THE AREA WEDNESDAY NIGHT
FOR SOME DRYING. STRONG LOW TO MOVE NORTH OUT OF THE NORTH PACIFIC TO
THE ALASKA PENINSULA THURSDAY WITH A STRONG FRONT MOVING TO KODIAK
AND TO THE KENAI PENINSULA THURSDAY AFTERNOON. WITH SOME STRONG UPPER
LEVEL SUPPORT WINDS WILL BE QUITE STRONG. AS THE FRONT WORKS TO THE
NORTHERN GULF COAST...WINDS TO PICK UP THERE WITH A ONSHORE RIDGE
DEVELOPING. THIS WILL ALSO ENHANCE EAST WEST ORIENTED PRESSURE
GRADIENTS ALONG THE COAST RESULTING IN INCREASED WINDS THROUGH
CHANNELED TERRAIN. THE LOW TO LIFT INLAND WEST OF THE ALASKA RANGE
THURSDAY NIGHT WITH EAST WEST GRADIENT DIMINISHING ALONG THE COAST
FRIDAY MORNING. WINDS WILL BECOME STRONG ONSHORE BEHIND THE LOW
SPREADING PRECIPITATION ALL OVER SOUTH CENTRAL ALASKA. DUE TO THE
STRENGTH OF THE LOW AND THE WINDS ALOFT AROUND IT...STRONG SURFACE
WINDS CAN ALSO BE EXPECTED BEHIND THE FRONT INTO FRIDAY EVENING EVEN
THOUGH THE LOW CENTER WILL BE NEAR THE BROOKS RANGE. SHOWER ACTIVITY
TO WANE SATURDAY AS THE LOW EXITS TO NORTHERN CANADA. AT THIS
TIME...ANOTHER LOW RACES INTO THE GULF ALONG TAIL OF THE JET AXIS TO
THE NORTHERN GULF COAST SUNDAY NEAR YAKUTAT.

SURFACE WEST OF THE ALASKA RANGE...LOW NEAR KODIAK WITH PLENTY OF
PRECIPITATION AROUND THE LOW IN SOUTHWEST ALASKA. THE LOW WILL MOVE
INTO THE GULF TONIGHT. HOWEVER...STRONG GRADIENT OVER THE EASTERN
BERING WILL KEEP THE CURRENT MODERATE NORTHERLY SURFACE WINDS THERE.
WINDS THOUGH TURN MORE WESTERLY BEHIND THE LOW. IN ADDITION...A WEAK
LOW MOVING SOUTH THROUGH THE BERING SEA TONIGHT HAS SOME MODERATE
NORTHERLY WINDS AS WELL. THIS LOW TO DISSIPATE TOMORROW AS A STRONG
LOW MOVES OUT OF THE NORTHERN PACIFIC TOMORROW AFTERNOON AND EVENING.
THIS LOW DEEPENS AS IT MOVES TO THE ALASKA PENINSULA THURSDAY
AFTERNOON. VERY STRONG WINDS AND HEAVY PRECIPITATION ARE ANTICIPATED
AROUND THIS LOW ESPECIALLY ON THE EAST SIDE WHERE STRONG JET SUPPORT
AND WARM FRONT PRESENT. MODERATE WINDS ON THE BACKSIDE OF THE LOW IN
THE BERING SEA. THIS LOW MOVES INLAND THURSDAY NIGHT AND NEAR THE
BROOKS RANGE FRIDAY. HOWEVER...IT DOMINATES THE WEATHER INTO FRIDAY.
HIGH PRESSURE MOVES OVER THE ALEUTIAN CHAIN BEHIND THE LOW FRIDAY
WITH MODERATE WINDS REMAINING BEHIND THE LOW IN THE EASTERN BERING
AND SOUTHWEST ALASKA.  THE LOW LEAVES THE AREA SATURDAY WITH RESIDUAL
MOISTURE OVER SOUTHWEST ALASKA FOR SHOWERS. HIGH PRESSURE IS OVER THE
BERING AT THIS TIME WITH A NEW LOW MOVING FROM THE WEST SOUTH OF THE
WESTERN ALEUTIAN CHAIN INTO SUNDAY.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE
MARINE...GALE 155 165 170
FIRE WEATHER...NONE

JN SEP 06